Most strokes are caused by thromboembolic occlusion in major or smaller intracerebral arteries (Wardlaw, Murray et al. 2009). In ischemic stroke, rapid thrombolysis is the only established therapeutic option to suppress the onset of unavoidable complete infarction (1995; Choi and Bateman et al. 2006). Treatment through the intravenous administration of recombinant tissue plasminogen activator (r-tPA) is currently the only approved therapy for ischemic stroke, which can be made within 4.5 hours after the onset of ischemic stroke (Caplan, Mohr et al. 1997; and Lopez-Yunez, Bruno et al. 2001). However, more than half the patients failed to achieve successful recanalization after thrombolytic treatment (Rha and Saver 2007; and Lee et al. Stroke 2007; 38:192-193]. Even if occluded arteries are successfully recanalized by the thrombolytic treatment, these benefits are again degraded due to the risks of reperfusion injury (Hallenbeck and Dutka 1990), intracerebral hemorrhage (Adams, Adams et al. 2005), and reocclusion (Heo, Lee et al 2003). In addition, rt-PA was reported to have neurotoxicity (Chen and Strickland 1997; Wang, Tsirka et al. 1998; Nicole, Docagne et al. 2001; Yepes, Sandkvist et al. 2002; and Matys and Strickland 2003).
Although the recanalization strategy has proven its efficacy, it caused limited applicability and potential adverse effects, and thus there have been efforts to develop new thrombolytic agents having better effects than rt-PA. These efforts include variants of t-PA, plasminogen activators derived from animal sources, and microplasmin. The above-cited drugs have the following purposes: (a) enhancing fibrin specificity; (2) extending plasma half-life; (3) reducing inhibitory ability by plasminogen activator inhibitor-1; and (d) avoiding neurotoxicity. Several drugs have completed clinical trials, and some drugs are being studied for their efficacy. These drugs target fibrin in the thrombi, and thrombolytic agents, such as rt-PT and urokinase, correspond to these drugs. However, the thrombi are formed by a platelet-fibrinogen interaction. Thrombin, leukocytes, and erythrocytes are also components of the thrombus. The resistance of the thrombi to the thrombolytic agents targeting fibrin is one of the main causes of low recanalization rates in stroke patients, which may occur more commonly in occlusion by platelet-rich thrombi. In this regard, the treatment targeting platelets may be an option or additive to the treatment targeting fibrin for improved thrombolytic efficacy.
Platelet glycoprotein (GP) IIb/IIIa, a member of the integrin family, exists on the surface of the platelet membrane at high density (Shattil and Ginsberg 1997). The GPIIb/IIIa receptor mediates the final stage of the platelet aggregation pathway by specifically binding to fibrinogen (Phillips, Charo et al. 1988). Therefore, targeting the platelet GPIIb/IIIa receptor has been the mainstay for the development of drugs acting on the platelets. Many platelet GPIIb/IIIa antagonists have been developed, which include the Fab fragment of a human-mouse chimeric antibody against GP IIb/IIIa (abciximab), nonpeptide analogues of RGD peptides (tirofiban and lamifiban), and cyclic heptapeptide disintegrin containing KGD motif (eptifibatide) (Seitz, Meisel et al. 2004; Abou-Chebl, Bajzer et al. 2005; and Eckert, Koch et al. 2005). These GPIIb/IIIa antagonists have been effective for patients with unstable angina, acute myocardial infarction, and percutaneous treanfemoral coronary angioplasty (PTCA) and patients receiving stent. In stroke, abciximab failed to show efficacy in patients who were treated 5 to 6 hours after the symptom onset (Adams, Effron et al. 2008). However, GPIIb/IIIa antagonists lyse the thrombi in stroke patients with reocclusion, and are effective for selected patients (Heo, Lee et al. 2003; Seitz, Hamzavi et al. 2003; Seitz, Meisel et al. 2004; Eckert, Koch et al. 2005; and Chen, Mo et al. 2007).
Saxatilin, which is a novel disintegrin that is purified and cloned from Korean snake venom, has the tripeptide sequence Arg-Gly-Asp (RGD), which is a recognition site of disintegrin to the platelet GPIIb/IIIa receptor (Hong, Koh et al. 2002; and Hong, Sohn et al. 2002). It has been known that saxatilin has strong inhibitory effects on platelet aggregation (Hong, Koh et al. 2002) and platelet activation (Jang, Jeon et al. 2007), and thus interrupts the generation of thrombus.
Throughout the entire specification, many papers and patent documents are referenced and their citations are represented. The disclosure of the cited papers and patent documents are entirely incorporated by reference into the present specification and the level of the technical field within which the present invention falls, and the details of the present invention are explained more clearly.